How to Run a Jar Test for PAC/PACS Coagulant Selection
Jar testing is the standard bench-scale tool used to compare coagulation-flocculation-settling behavior. There is no single universal mixing protocol; the most useful procedure is one that reproduces the plant’s real hydraulic conditions as closely as practical.
1. Characterize the raw water first
Record at least pH, temperature, alkalinity and turbidity. Add conductivity, TOC/UV254 and suspended solids when available. Coagulant demand can shift as raw-water quality changes.
2. Build a meaningful dose sweep
Compare 5-6 coagulant doses on the same raw water. When PAC and PACS have different active content, normalizing on an active Al/Al₂O₃ basis can be more meaningful than comparing commercial product mass alone.
3. Reproduce the mixing sequence
Rapid mix simulates fast coagulant dispersion, followed by lower-shear flocculation and then settling. Time and rpm should be adapted to the plant rather than treated as universal constants.
4. Look beyond turbidity
In addition to treated-water turbidity, evaluate floc size/strength, settling behavior, pH, residual aluminum and sludge volume where relevant. The optimum balances water quality and chemical consumption.
5. Run a second optimization around the best PACS range
After the first screening, retest a narrower range around the best 2-3 doses. Add pH screening where needed. This verifies high-basicity PACS against the actual water matrix.